Endfire array



July 2, 1963 w. EHRENSPECK 3,096,520

ENDFIRE ARRAY Filed March 6, 1958 v 2 Sheets-Sheet 1 HERMANN WE|W80K WWM MM/VAV ATTORNEYS y 1963 H. w. EHRENSPECK 3,096,520

ENDFIRE ARRAY .Filed March 6, 1958 2 Sheets-Sheet 2 o o o o o 0 2O 0 o oo o o o o o 0 \2"-0 O O o o o o 0 o icyo o b o o o o o o o o o o o o w 3o o o o o o o QZB o o o o o o o o o 0 2 0 o o o 0 INVENTOR. HERMANNW.EHRENSPECK ML...- q

AT ORNEYS United States Patent 3,096,520 ENDFIRE ARRAY Hermann W.Ehrenspeck, 94 Farnham St., Belmont 78, Mass. Filed Mar. 6, 1958, Ser.No. 719,698 2 Claims. (Cl. 343-834) (Granted under Title 35, US. Code(1952), sec. 266) t The invention described herein may be manufacturedand used by or for the United States Government for governmentalpurposes without payment to me of any royalty thereon.

This invention relates generally to antennas and more particularly to amethod and means for controlling the amplitude and phase across avirtual aperture.

Endfire arrays, such as Yagi antennas, may be analyzed in terms of theamplitude and phase distribution in a virtual aperture plane transverseto the array axis and located at the end of the array. Arrays of thistype usually have high side lobes like horns which, according to myinvention, may be reduced by afiecting the amplitude and phasedistribution in the virtual aperture of the endfire array.

According to the teachings of my invention, both amplitude and phasedistribution may be aifected by placing one or more parasitic side rowson both sides of the center array, thus transforming the array into atwo-dimensional array.

The utilization of the parasitic arrays of my invention provide areduction in side lobes, increased gain, and increased bandwidth withrespect to pattern.

It is, therefore, an object of my invention to produce a novel methodand means for reducing side lobes of an antenna pattern.

It is another object of my invention to produce a novel endfire arrayhaving good side lobe reduction and increased gain.

It is still another object of my invention to produce a novel method andmeans for increasing antenna bandwidth with respect to pattern.

It is a further object of my invention to provide a novel method andmeans for producing side lobe reduction which may be applied to existingendfire arrays.

It is a still further object of my invention to produce \a novel meansfor side lobe suppression not requiring additional feed systems.

Another object of my invention involves the utilization of parasiticside rows to a center array in the vertical as well as horizontaldirection to improve pattern and gain performance.

Still another object of my invention involves the utilization of \anovel means for side lobe reduction applicable to both high and lowfrequency antennas.

A further object of my invention involves the production of an antennasuitable for use for scatter propagation.

These and other advantages, features and objects of the invention willbecome more apparent from the following description taken in connectionwith the illustrative embodiments in the accompanying drawings, where-FIGURE 1 is a representation of an antenna array with two parasitic siderows;

FIGURE 2 is a plan view of a two-dimensional endfire array with sixparasitic side rows;

FIGURE 3 is an end view of a three-dimensional endfire array; and

FIGURE 4 is a schematic representation of an arrangement for renderingthe parasitic arrays suitable for scatter propagation.

The end of an array may be considered to be a 3,096,520 Patented Jul 2,1963 radiating aperture, and, because there are no physical -may beaccomplished by changing the width of the virtual aperture and theamplitude and phase distribution within said aperture. An array changefrom single to two-dimensional allows an increase in gain by increasingthe virtual aperture; reducing side lobes by changing amplitude andphase distribution within said aperture; and simultaneously increasinggain and achieving side lobe reduction by changing both aperturedistribution and width.

Referring to FIGURE 1, a ground plane 10 may be used, although it doesnot form a necessary part of my invention. Mounted on the ground plane10 is :an example of an endfire antenna shown as a Yagi array 11 ofmonopoles with a reflector 12. A coaxial feed means 13 excites the arrayfrom beneath the ground plane.

It was found that the width of, and distribution in the virtual apertureat effective energy levels can be changed in the desired manner bysymmetrically placing one or more shorter rows of parasitic elements 14and -15 V on either side of the center :array. The utilization of anon-symmetrical arrangement produces a change in pattern. Parasitic siderows :14 and 15 act as smaller wave channels fed mainly by coupling fromthe main center array 11 which results in a two-dimensional parasiticendfire array excited by a single feed 13 of the main array 11.

The dotted line portion represents an aperture plane with arbitrarylimits of 20 db of maximum power level in the vertical and transversedirections.

Side rows '14 and 15 are adjusted so that the phase front in the virtualaperture is as uniform as possible and the amplitude distribution isgiven the form needed for a specified pattern. Phase may be controlledby adjusting the phase velocity which depends on the spacing, height,and diameter of the parasitic elements. An infinite number ofcombinations of these parameters may be used to achieve a desired phasevelocity. Amplitude may be controlled by variation of side row length.The adjustments of the phase front and amplitude distribution can beperformed, within limitations, relatively independently of each other.

In order to couple sufiicient energy to the side arrays 14 and 15, theusual placement of these arrays falls within the virtual aperture. Thephase deviation in the virtual aperture of the center array 11 withoutthe parasitic side rows undulates and side row placement is usually madeat the point of maximum deviation; however, adjustment of the variousparameters allows a placement anywhere within the virtual aperture andeven slightly outside it depending on the amount of coupling energydesired.

Tests made on the array of FIGURE 1 indicate an increased gain of 30%and an increased virtual aperture of 37% using the following exemplaryphysical dimensions:

Element diameter .04 8x FIGURE 2 is a top view of an antenna having acenter array 11 with reflectors 12, a feed 13 and six side rows 16, 1'7,18, 119, 20, and 21 wherein the virtual aperture is increased by 66%above the Yagi type endfire array, and the measured gain increase is60%.

An extension of the principle of this invention to increase the heightof the virtual aperture in the vertical direction would be to place sidearrays above (and below if there is no ground plane) the center array11. By thus passing from a two-dimensional to a three-dimensional arraya further increase in gain results. FIG- URE 3 is a representation of anend view of a threedimensional antenna having a central Yagi array 11and parasitic arrays 22, 23, 24 and 25. Of course the absence of aground plane indicates the use of dipoles rather than monopoles in thisembodiment. Since the parasitic arrays do not act as reflectors, theheight of the elements of the arrays will be less than a quarterwavelength for monopoles and a half wavelength when dipole elements areused.

Thus, the performance of an endfire array may be explained relative tothe concept of a virtual aperture located at the end of the array, andaccomplishment of control of this aperture by coupling energyparasitically from the main array into adjacent side rows.

Utilization of the teachings of my invention produce changes in sidelobe level and gain, simultaneously. These accomplishments are obtainedby low cost antenna construction without an appreciable increase inspace compared with conventional endfire arrays of the same length.Furthermore, the initial feed system can be used without complicatedpower distribution networks common to other antennas capable ofproducing comparable results.

Non-symmetrical arrangements of the parasitic arrays fall within thescope of my invention in that assymetry produces a change in the patternof the resutling beam; therefore, it follows that a sweep for scatterpropagation may be achieved by changing the phase by changing the heightof the parasitic array; e.g., by attaching the 4! monopoles to a singlesupport and moving the elements through the ground plane and controllingthe height by means of an eccentric or cam acting on said support. or byrotating the dipoles of the parasitic side rows, which, in effect,change their electrical length.

Although the invention has been described with reference to particularembodiments, it will be understood to those skilled in the art that theinvention is capable of a variety of alternative embodiments within thespirit and scope of the appended claims.

I claim:

1. A method for controlling the side lobe and gain characteristics of anendfire antenna array by controlling the virtual aperture of the arraycomprising the steps of placing parasitic arrays about said endfirearray adjusting the phase distribution in the virtual aperture byvarying the height, spacing and diameter of the parasitic elements ofsaid parasitic arrays, and adjusting the amplitude within said virtualaperture by varying parasitic array length.

2. An endfire antenna array comprising a main endfire antenna, and aseries of parasitic arrays located symmetrically about said main endfireantenna at points of maximum phase deviation in the virtual aperture ofsaid main endfire antenna.

References Cited in the file of this patent UNITED STATES PATENTS1,860,123 Yagi May 24, 1932 2,199,050 Jenkins Apr. 30, 1940 FOREIGNPATENTS 399,770 Great Britain Oct. 12, 1933 OTHER REFERENCES BeamAntenna Handbook, by W. I. Orr, copyright 1955, pages 2224 TK 7872 A607.

Silver, 8.: Microwave Antenna Theory and Design, I 1949, published byMcGraw-Hill Book Company, Inc.,

New York, N.Y., pages 158, 159, 179, 180.

1. A METHOD FOR CONTROLLING THE SIDE LOBE AND GAIN CHARACTERISTIC OF ANENDFIRE ANTENNA ARRAY BY CONTROLLING THE VIRTUAL APERTURE OF THE ARRAYCOMPRISING THE STEPS OF PLACING PARASITIC ARRAYS ABOUT SAID ENDFIREARRAY ADJUSTING THE PHASE DISTRIBUTION IN THE VIRTUAL APERTURE BYVARYING THE HEIGHT, SPACING AND DIAMETER OF THE PARASITIC ELEMENTS OFSAID PARASITIC ARRAYS, AND ADJUSTING THE AMPLITUDE WITHIN SAID VIRTUALAPERTURE BY VARYING PARASITIC ARRAY LENGTH.